1. Field of the Invention
The present invention relates to a hermetic compressor, and more particularly to a hermetic compressor having an improved structure for reducing the noise generated during operation of the compressor.
2. Description of the Related Art
Generally, as shown in FIG. 1, a hermetic compressor includes a sealing case 1, an electric drive portion 10 formed in the case 1, and a compression portion 20. The electric drive portion 10 generates a driving force that reciprocates linearly to compress a refrigerant in the compression portion 20. The electric drive portion 10 includes a rotor 11 and a stator 12.
The case 1 includes a lower shell 1a and an upper shell 1b. A rotary shaft 14 having an eccentric portion 13 is press fit on the rotor 11. The compression portion 20 includes a cylinder 21 having a suction port 21a and a discharge port 21b, a piston 22 that linearly reciprocates within the cylinder 21, and a connecting rod 23 disposed between the piston 22 and the eccentric portion 13 of the rotary shaft 14. As the rotary shaft 14 rotates along with the rotor 11, the piston 22 reciprocates within the cylinder 21. The movement of the piston 22 causes the refrigerant to be repeatedly drawn in and discharged through the suction port 21a and the discharge port 21b. 
A compressor having the above structure is usually employed in household refrigerators, and its quality depends mainly on the following two factors: the compression efficiency; and how quiet the compressor is during operation. More specifically, as the compressor operates, various levels of cavity resonance are generated due to the temperature and pressure in the case 1. When the cavity resonance equals the resonance frequency of the case 1, it generates unpleasant sounds, and the compressor vibrates severely. It is evident that such vibration and noise from the compressor affect the quality of the refrigerator. More serious noise is produced from the upper portion of the upper shell 1b, which makes high-pitched, metallic, trembling sounds in the high frequency range of 3100 Hz to 3300 Hz. It is noise in this frequency range that has to be particularly controlled.
Because the resonance, which is the main source of the noise, is generated at various frequency ranges, it has been difficult to design a compressor that could prevent noise across a broad range, spanning from the cavity resonance range to resonance frequency range. Recently, the suggestion has been made to vary the thickness of the case 1 to vary the cavity resonance from the resonance frequency range. The suggestion, however, leads to problems, such as difficult and complex design of the compressor and a thicker case 1.
The present invention has been made to overcome the above-mentioned problems of the related art. Accordingly, it is an object of the present invention to provide a hermetic compressor having an improved structure for reducing noise that is generated during operation of the compressor.
The above object is accomplished by providing a hermetic compressor including an electric drive portion, a compression portion and a casing. The electric drive portion has a rotor and a stator and generates a driving force to compress a refrigerant in the compression portion. The casing encloses the electric drive portion and the compression portion. The compressor further includes a unit process portion formed on an upper portion of the casing. The unit process portion is processed to have a circular or a polygonal shape from a front view. The unit process portion increases a rigidity of the casing, thereby reducing the amount of noise that is generated from the electric drive portion and the compression portion during an operation of the compressor.